This invention relates to MOSgated devices and more specifically relates to a novel super junction-type device and method for its manufacture, which has a low on-resistance and high breakdown voltage.
MOSgated devices such as power MOSFETs, IGBTs, and gate turn on thyristors are well known. A typical MOSgated device of this type is shown in U.S. Pat. No. 5,007,725. These devices may be made with a closed cellular base or spaced striped base topology. A device termed a COOLFET device made by Siemens Corporation, consists of a device in which spaced trenches form small width areas of increased conductivity epitaxially formed silicon. The higher conductivity epi reduces on-resistance, but is depleted under blocking voltage conditions to provide a high breakdown voltage. Such devices, termed superjunctions, are described in U.S. Pat. Nos. 4,754,310 and 5,216,275. This invention provides an improved device of the COOLFET type in which simpler manufacturing and improved operation is provided.
In accordance with the invention, a semi-insulating material, preferably a semi-insulating polysilicon or other non-injecting material fills vertically oriented parallel spaced trenches which extend completely through a depletable epitaxial silicon layer and reach, or are closely spaced from, the conductive silicon substrate which supports the epitaxial layer. The trenches could be lined with highly insulative silicon dioxide (to prevent injection) and then filled with conventional conductive polysilicon. A similar structure is used in termination of the chip.